Controlling Speciation during CO₂ Reduction on Cu-Alloy Electrodes

Electrodeposition of Cu, Cu/Ag, and Cu/Sn alloy films by using 3,5-diamino-1,2,4-triazole (DAT) as an electrodeposition inhibitor yields a high surface area Cu-based catalyst. All three Cu-based electrodes exhibit high Faradaic efficiency (FE) of CO 2 reduction toward C 2 H 4 production. The CuSn-DAT electrode exhibits the highest FE for CO (∼90% at −0.4 V) and C 2 H 4 (∼60% at −0.8 V) production and high current density (∼−225 mA/cm 2 at −0.8 V). In situ surface enhanced Raman spectroscopy (SERS) studies in a flow cell obtained from the three Cu-based samples show a correlation between the decreased oxide content on the Cu surface, increased presence of CO, and increased activity for CO and C 2 production. The CuSn-DAT electrode has the lowest amount of Cu 2 O and exhibits the highest activity, whereas the Cu-DAT electrode has an increasing Cu 2 O content and exhibits lower activity as the potential is made negative. These results demonstrate that incorporation of different well-mixed alloy materials provides a way to tune CO 2 reduction speciation.